1. Field of the Invention
The invention relates generally to wireless communication and more particularly to systems and methods for obtaining position information using a wireless communication device.
2. Background
A traditional Global Positioning Technology (GPS) receiver receives and processes specially coded satellite communication signals. The Satellite signals are generated from an array of satellites that comprise the GPS system. Nominally, this array consists of 24 satellites arranged in various orbits such that between 5 and 8 satellites are visible from any point on earth. GPS receivers convert the satellite signals into position, velocity, and time estimates. Four satellites are required to compute the three position dimensions (x,y,z) as well as the time.
Today, GPS capability is frequently added to wireless communication handsets. Unfortunately, the GPS signals operate at different frequencies than those used for typical wireless communication. GPS signals operate in the 1500 MHz band, while in the U.S., wireless communication systems generally operate in the 800 MHz and 1900 Mhz bands. As a result, the GPS signals cannot be received using a wireless communication handset's antenna and receiver. Therefore, in order to add GPS capability to a handset, a separate antenna and receiver must be included in the handset.
There are generally two conventional ways to implement GPS capabilities in a wireless handset. The first is illustrated by exemplary communication system 100 in FIG. 1. System 100 comprises a wireless handset 106 in communication over communication channel 108 with a base station 110. By station 110, is, for example, at the center of a communication cell within a Wireless-Wide Area Network (W-WAN). Thus, handset 106 includes the requisite antenna and transceiver for communicating over communication channel 108. Again, communication channel 108 typically comprises signals in the 800 MHZ and/or 1900 MHz range.
Additionally, handset 106 is in communication with GPS satellites 102 over satellite communication channels 104. Thus, handset 106 also includes an antenna and associated GPS circuitry for receiving the satellite signals over satellite communication channels 104. In this implementation, the GPS circuitry decodes the satellite signals. The satellite signals are then sent to a Position Determination Entity (PDE) (112) interfaced with base station 110. PDE 112 determines the position of handset 106 from the decoded satellite signals and this information is transmitted back to handset 106, where it can, for example, be displayed n handset 106.
Thus, for example, if the subscriber wants to know his position, he can input a position request into handset 106. Handset 106 then acquires satellite signal information over satellite communication channels 104 using the GPS circuitry. The GPS circuitry decodes the satellite signals and handset 106 transmits the decoded signals to PDE 112 over communication channel 108. PDE 112 generates the position information from the decoded signals and transmits a position back to handset 106, where it is displayed to the subscriber on handset 106. PDE 112 can also be used to provide handset 106 with Access assist (AA) and sensitivity assist (SA) information to help handset 106 acquire satellites 102 over satellite communication channels 104.
By incorporating the GPS processing capabilities in PDE 112 instead of handset 106, the cost, complexity, and size of handset 106 can be reduced while offering enhanced GPS performance due to the greater computational power of the PDE. Since there is constant pressure to reduce the cost, complexity, and size of wireless communication headsets, this networked based approach has distinct advantages. There are, however, important disadvantages. First, for example, the network based approach increases the network traffic in system 100, which reduces system capacity, meaning fewer users can use the system. Second, the GPS capability only works when handset 106 is in range of system 100.
FIG. 2 illustrates a logical block diagram of an exemplary wireless handset 200 that can be used to illustrate a second way to implement GPS capabilities in a wireless handset, which overcomes the disadvantages of the implementation illustrated in FIG. 1. Handset 200 comprises an antenna 220 and wireless communication transceiver 224 configured to transmit and receive wireless communication signals, such as those that would be communicated over communication channel 108 in FIG. 1. Wireless communication transceiver 224 comprises receiver 216, which is configured to receive wireless communication signals from antenna 220, filter and amplify them, and then send them to demodulator 218. Demodulator 218 demodulates the received signal in order to generate a baseband information signal that is sent to modem 212. Historically, a modem comprised a modulator and a demodulator. However, a common definition for a modem is simply a modulator coupled with some signal processing functions. Within this patent, a modem is defined as modulator coupled with a processor. Transceiver 224 also includes transmitter 214, which is configured to transmit wireless communication signals via antenna 220 generated by Modem 212.
Typically, demodulator 210 comprises two stages; the first stage steps the frequency of a received signal down from a Radio Frequency (RF), used for transmitting signals over channel 108, to an Intermediate Frequency (IF). The IF frequency signal is then stepped down, in the second stage of demodulator 218, to baseband.
Modem 212 preferably includes various circuits for controlling the operation of handset 200 in general, and in particular for controlling communication using transceiver 224. Thus, Modem 212 can include various analog-to-digital (A/D) and digital-to-analog (D/A) converters, processors, Digital Signal Processors (DSPs), Vocoders, and peripheral control circuits as required by a particular handset 200. Alternatively, some or all of these circuits can be included in handset 200 as stand alone components or as components incorporated into the various components of transceiver 224.
In addition, handset 200 includes GPS processor 208 configured to process GPS signals received via antenna 202, which are filtered and amplified in GPS receiver 204 and demodulated in GPS demodulator 206. Thus, GPS processor 208 can generate position information when requested without the aid of a network based position determination. Accordingly, the implementation of FIG. 2 overcomes the problems associated with network position determination, such as increased traffic and a limited operating range. But, as mentioned, including a full GPS receiver in handset 200 drives up the cost, complexity, and size of handset 200 and can also have other negative affects such as reduced battery lifetime. As such, neither of the conventional solutions for incorporating GPS into a wireless communication handset is satisfactory.